This invention relates generally to the switching of polarization in a ferroelectric structure and relates, more particularly, to the switching of the direction of polarization in a thin-film ferroelectric structure by way of an electrically-chargeable conducting tip that can also exert local force.
The polarization of ferroelectric material in a thin film ferroelectric structure can be switched with the cantilevered and conductive tip of an Atomic Force Microscopy (AFM) instrument by electrically charging the tip and then moving the tip into contact with the surface of the ferroelectric structure. Such action exemplifies a technique for switching a direction of polarization of ferroelectric material in a ferroelectric data storage device. For example, if the direction of polarization of the ferroelectric material in a ferroelectric data storage device store information corresponding with either a or a “+” or either a “−” or a “0”, by bringing an appropriately-charged tip of an AFM into contact with the surface of the memory device, the direction of polarization of the ferroelectric material is reversed so that the information becomes either a “−” or a “+” or either a “0” or a “1”.
Heretofore, however, the region (i.e. domain) of the ferroelectric material which is affected, or switched, by the electrically-charged tip of the AFM is appreciably larger than the area of contact between the AFM tip and the surface of the ferroelectric structure. Such a consequence is believed to be due, at least in part, to the proximity between the portions of the surface of the ferroelectric structure which are not in contact with the AFM tip and the electrostatic fields which surround the electrically-charged tip. In any event, these long range interactions limit the minimal domain size that can be achieved during a switching operation performed with the AFM tip. Since domain size directly controls the amount of information which can be stored in a ferroelectric structure, it would be desirable to provide a scheme for switching the direction of polarization in a ferroelectric material wherein only a relatively small domain within the ferroelectric material is affected.
Accordingly, it is an object of the present invention to provide a new and improved method for switching the direction of polarization in a ferroelectric material with an electrically-chargeable tip wherein the size of the affected domain is relatively small.
Another object of the present invention is to provide such a method wherein the size of a domain affected by the electrically-chargeable tip corresponds to about the size of the surface area of the ferroelectric material contacted by the tip.
Still another object of the present invention is to provide such a method for inducing high order ferroelectric switching.
Yet another object of the present invention is to provide such a method that allows for the creation and detection of domains at nanometer length scale and whose domain size can be determined quantitatively.
A further object of the present invention is to provide such a method which is well-suited for use in applications such as may involve ultrahigh density storage, ferroelectric lithography or nanostructure fabrication.
A still further object of the present invention is to provide such a method which is relatively easy to perform yet effective in operation.